Tamper respondent enclosures are used in various applications, including the transport of sensitive information and protecting electronic devices. Typical enclosures are in the form of envelopes and shallow boxes, the walls of which are formed by folding flexible sheets incorporating tamper detection features. As used herein, sheets incorporating tamper detection features are known as “sensors”. These sheets may also be wrapped around preexisting boxes or enclosures.
Included in such sheets are layers of flexible material and a matrix of diagonally extending or zig-zag pattern semi-conductive or conductive lines, also known as conductive traces. The lines or traces are printed on thin insulating film. The matrix of lines forms a continuous conductor which is broken if attempts are made to penetrate the film. The sensor matrix is monitored and when a tamper occurs the electrical state of the sensor changes. A detection of a change in state can initiate a signal. This signal can erase information stored within the enclosure, or otherwise protect the information from being discovered.
In known devices, the matrix of semi-conductive or conductive lines or traces on the insulating film is printed on both sides of the film. The lines on one side are disposed in the sections of the film opposite from where the lines are disposed on the opposite side. In this manner, complete coverage of the film is obtained, and it is more difficult to penetrate the film without cutting a line, either on one side of the film or the other.
Typically, the flexible material is a clear insulating film such as PET. In order to further protect and obfuscate the location of the lines of the semi-conductive lines, thereby making it more difficult to circumvent them in an attempt to break through the film to get to the information, known methods include a potting material. This potting material is typically a dark resin that encapsulates the entire film. The dark potting material provides a mechanical barrier and hides the location of the semi-conductive lines.
Although these devices are effective, they are difficult to manufacture. A construction that leads to a more efficient assembly is desired.